let table = [0, 0, 0, 0]; for (let i = 0; i < journal.length; i++) { let entry = journal[i], index = 0; if (entry.events.includes(event)) index += 1; if (entry.squirrel) index += 2; table[index] += 1; } return table; } console.log(tableFor("pizza", JOURNAL)); // → [76, 9, 4, 1]
Arrays have an includes method that checks whether a given value exists in the array. The function uses that to determine whether the event name it is interested in is part of the event list for a given day. The body of the loop in tableFor figures out which box in the table each journal entry falls into by checking whether the entry contains the specific event it’s interested in and whether the event happens alongside a squirrel incident. The loop then adds one to the correct box in the table. We now have the tools we need to compute individual correlations. The only step remaining is to find a correlation for every type of event that was recorded and see whether anything stands out.
Array loops In the tableFor function, there’s a loop like this: for (let i = 0; i < JOURNAL.length; i++) { let entry = JOURNAL[i]; // Do something with entry }
This kind of loop is common in classical JavaScript—going over arrays one element at a time is something that comes up a lot, and to do that you’d run a counter over the length of the array and pick out each element in turn. There is a simpler way to write such loops in modern JavaScript. for (let entry of JOURNAL) {
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